This is the first in a series exploring the basic principles of permitted development – i.e the parliament granted right to make certain changes and modifications to your home without going through the planning application process. We are going to start simple and establish what can and can’t be done with a single storey extension.


So….. you want to build an extension?


Great – but now what! It can seem like this is the only easy part of the decision – from here on in it’s a minefield of information, possibilities and choices. Who to notify? What are the rules? How much will this all cost? However, this doesn’t have to be such a daunting prospect – bear in mind the following key points and this can help simplify the initial decision process and help you create your new space.


I always find the best starting place is to assume that the extension is classed as permitted development, and then work through the list of conditions below. Simply put, if the proposal fits with all the conditions, then it’s most likely that it is permitted development, if however it doesn’t fit with even one of the conditions, then it’s almost certain that a planning application will be needed.


  • The property does not fall within a designated area – these are things like sites of special interest, national parks and similar
  • Your extension and any other buildings on the site (garages sheds etc) can not account for greater than 50% of the land surrounding the house when it was originally built, or as it stood in 1948
  • If your extension is going to be on the front or the side facing a highway – it will not come under the permitted development laws.
  • The materials that you aim to use should be in keeping with that of the original development – however a conservatory type structure is exempt from this principle.
  • If you are going with a side extension, you can’t make it more than half the width of the original building and/or greater than 4 metres high.
  • If you are going backwards – so to speak – you can not have an extension that goes back further than 3 metres if you are attached, and 4 metres if you are detached. In either case you not go upwards to a height greater than 4 metres. However, if your extension is to be built prior to May 2019, and you aren’t in a designated area – these distances are increased to 6 and 8 respectively – but will come under the neighbour consultation scheme.
  • In addition if your extension is going to come within 2 metres of the property boundary, the height of the eaves cannot be higher than 3 metres. Regardless of the distance from your boundary the eaves cannot be any higher than those of the original building.


Basically these factors allow quite a bit of scope in improving the average residential dwelling and a significant number of proposals come under the permitted development legislation. However, if you feel that you are an exception to the above rules – don’t despair! A professional in architecture will be able to advise you and help you – either in tailoring your vision to meet permitted development or by helping with the planning process.

In most cases, I would advise that even if you think your proposal does fall under permitted development, that you apply for a “certificate of lawfulness” This will allow the planning authority to look at the proposal and confirm whether or not a planning application is required.


These factors are just a guide and as with anything in life there are always exceptions and specifics to the rule. Lacey Architectural Services can offer you a free initial consultation, where Zak will visit your property and help you envisage schemes that can help your home realise its potential.